Passenger aircrafts are designed to meet numerous safety guidelines and regulations. These requirements are designed to ensure the general safety of passengers and crew. For example, current U.S. regulations relating to fuselage passenger entry doors include requirements that all such doors remain closed, latched, and locked and that an individual lock is provided for each door latch. The regulations further require that each door have a means for direct visual inspection to determine, without ambiguity, if the door is fully closed, latched, and locked. This means for visual inspection is required to be discernible from various viewing angles under operational lighting conditions, which may include light sources as varied as, for example, direct sunlight and a flashlight.
Often, such safety requirements may pose a nuisance to the passengers or crew of the aircraft. In some cases, methods for complying with these regulations require additional labor to be performed by the service crew. In other instances, safety regulations subject the passengers to noise or light disturbances. For example, the requirement for a visual inspection means of the closed, latched, and locked conditions of fuselage doors is typically met using mechanical means, such as a lever arm, the position of which indicated the status of a particular door. The lever arm is a relatively simple mechanism, but still requires the action of the crew to report its status and further adds the weight of the mechanism at each door to the overall weight of the aircraft.